A filtering apparatus of this class is disclosed in DE 10 2007 054 737 A 1. Such a filtering apparatus allows for continuous filtration operation. Successive filtering elements that must be regenerated are back-flushed, while the filtration operation is continued by the remainder of the filtering elements, such that the filtration operation is never interrupted.
In the known filtering apparatus, the back-flushing operation does not only occur in such a manner that, during the back-flushing phase, the system pressure, which is present inside the filtering apparatus, causes a partial flow of the filtrate to flow in the reverse direction through the filtering element that is to be cleaned to loosen and remove dirt from the element. Instead, with the goal of being able to remove more persistent impurities as well, a pressure-control is used on the respective filtering element that is to be back-flushed in order to create a vacuum. Therefore, the back-flushing operation is not only subject to the effective system pressure, but also to the effect of the pressure control, whereby a higher pressure gradient is available for loosening impurities.
On the filtering apparatus that is known in the art, the pressure-control device includes a blocking element that is able to block the fluid connection between the fluid that flows into the filter housing and that is to be filtered and the respective filtering element that is to be back-flushed during a back-flushing operation. Prior to the back-flushing process, this blocking element results in an interruption of the fluid flow that enters the filtering element, such that the flow rate, which is in effect at the time of the locking process, generates, by way of a flow-dynamic effect, a suction effect. Consequently, the back flow of the filtrate on the clean side of the respective filtering element is not only supported by the system pressure, but the back-flow of the filtrate is intensified by the post-suction effect, which is available due to the dynamic effect resulting from blocking out the flow that flows in from the untreated side.
However, the magnitude of the hydrodynamic effect that is achieved by the blocking process depends on the flow rate and is, therefore, correspondingly limited. In application fields where tough contaminations must be expected that are difficult to loosen from the filtering surface, the risk exists that the hydrodynamically supported back-flushing effect is not completely satisfactory.